New carbon data should produce better climate forecasts

Measurements for carbon dioxide input by plants and carbon dioxide released during respiration will help models

TURIN, Italy —
Climate change forecasts have always been afflicted by multiple sources of
uncertainty. Computer models are at the mercy of the data fed to them, and the
sources of the data aren’t always so reliable, leading to large variations in
forecasts of future temperatures. But now scientists have a little bit better
input on two important issues: the amount of carbon dioxide inhaled by land
plants and how respiration pumping CO2 back into the air depends on
temperature.

At a news conference July 5 in Turin, Italy — coinciding
with the Euroscience Open Forum conference — scientists from the Max Planck Institute for Biogeochemistry in
Jena, Germany, reported new findings from a global network of sensors called
Fluxnet. Data from the sensors indicate that land-based plants gulp down between
115 billion and 131 billion metric tons of carbon each year in the carbon
dioxide they consume during photosynthesis. Oddly enough, that’s pretty close
to the informed guesses that experts have been using in their climate modeling.
On the other hand, a separate but related study analyzing Fluxnet data found
that CO2 output back into the air by the respiratory processes of
living things is not as sensitive to temperature as scientists had been
assuming.

Respiration output isn’t easy to estimate, and field studies
have been in conflict with theoretical models on the effect of temperature on CO2
output, so that part of the global warming equation has contributed substantially
to the uncertainty in climate forecasts. Of particular concern was the
possibility that warming temperatures would elevate CO2 output by respiration
in a feedback loop leading to runaway temperature rise. But the new analysis
finds respiration to be less sensitive to temperature than some previous
analyses had suggested. Consequently the most dire scenarios of rapid warming
feedback now seem less likely.

With climate change science, though, no one new piece of
data produces a simple conclusion. For one thing, respiration rates are
complexly related to photosynthesis rates, and photosynthesis rates are
sensitive to rainfall, which is itself affected by changes in various factors
influencing climate.

“Climate change is not just global warming,” Markus Reichstein
of the Planck institute and a coauthor on both papers said at the ESOF news
conference. He said the new studies show that availability of water from
precipitation is much more important to the carbon budget in ecosystems than
has been generally recognized and warrants much more attention. And a lot of
carbon is stored in soils, with a potential for substantial feedback to the
atmosphere, he said.

So basically, the new studies (both published online July 5
in Science Express) do not change the
general picture on climate change, but do provide better data for refined
forecasts in the future.